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© 2000 ASM International. All Rights Reserved. www.asminternational.org ASM Specialty Handbook: , , and Their Alloys (#06178G)

Special-Purpose Nickel Alloys

NICKEL- ALLOYS have a number of meet special needs. The grades considered in ganese, and , a 0.005% limit on , and unique properties, or combinations of proper- this section include the following: a 0.02% limit on . This high purity re- ties, that allow them to be used in a variety of sults in lower coefficient of expansion, electri- specialized applications. For example, the high • Nickel 200 (99.6% Ni, 0.04% C) cal resistivity, , and greater resistivity (resistance to flow of electricity) and • Nickel 201 (99.6% Ni, 0.02% C maximum) than those of other grades of nickel heat resistance of nickel- alloys lead • Nickel 205 (99.6% Ni, 0.04% C, 0.04% Mg) and makes Nickel 270 especially useful for to their use as electric resistance heating ele- • Nickel 233 (see composition in table that fol- some electronics applications such as compo- ments. The soft magnetic properties of lows) nents of thyratrons and as a substrate nickel-iron alloys are employed in electronic • Nickel 270 (99.97% Ni) for precious cladding. devices and for electromagnetic shielding of computers and communication equipment. Iron- Composition limits and property data on sev- eral of these grades can be found in the article nickel alloys have low expansion characteris- Resistance Heating Alloys tics as a result of a balance between thermal ex- “Wrought Corrosion-Resistant and pansion and magnetostrictive changes with Nickel Alloys” in this Handbook. temperature. Originally used as clock pendu- Nickel 200 and 201. Wrought Nickel 200 Resistance heating alloys are used in many lums, these alloys are now widely employed as (UNS N02200), the general purpose grade, is varied applications—from small household ap- lead frames in packaging electronic chips and used for leads and terminals where good pliances to large industrial process heating sys- as the shadow-masks in color television tubes. strength and toughness at elevated temperature tems and furnaces. In appliances or industrial On a larger scale, they provide one solution to and subzero temperatures are necessary; for process heating, the heating elements are usu- transducers (it being one of three dem- coping with the require- ally either open helical coils of resistance onstrating magnetostrictive properties); and for ments of storage and transportation tanks for mounted with ceramic bushings in a suitable fuel cell and battery plates. the growing liquid natural gas industry. metal frame, or enclosed metal-sheathed ele- A low-carbon variant, Nickel 201 (UNS Other properties of interest that expand the ments consisting of a smaller-diameter helical N02201), is ideal for deep drawing, etching, markets and applications of nickel and nickel coil of resistance wire electrically insulated spinning, and coining; its rate of work harden- alloys include those to follow: from the metal sheath by compacted refractory ing is also low. insulation. In industrial furnaces, elements of- The selected chemistry of • Shape memory characteristics of equiatomic Nickel 205. ten must operate continuously at temperatures Nickel 205 (UNS N02205) results in a high nickel- alloys that allow them to be as high as 1300 °C (2350 °F) for furnaces used magnetostrictive coefficient and Curie temper- used as actuators, hydraulic connectors, and in metal-treating industries, 1700 °C (3100 °F) ature. Its uses have included grid side rods, eyeglass frames for kilns used for firing ceramics, and occasion- base pins, anodes, getter tabs, and • The high strength at elevated temperature ally 2000 °C (3600 °F) or higher for special ap- shields. and resistance to stress relaxation that allow plications. (UNS N02233) is specially pro- wrought nickel--titanium to be Nickel 233 Material Requirements. Materials for elec- duced to the following closely controlled, low- used for demanding electrical/electronic ap- tric heating depend on an inherent resistance to plications, for example, springs subjected to the flow of electricity to generate heat. Copper wire does not get appreciably hot when carry- elevated temperatures (up to 370 °C, or 700 Element Percentage °F) for short times ing electricity because it has good electrical • Carbon 0.15 max The combination of heat removal (high ther- Copper 0.10 max conductivity. Thus for an —as wire, rib- mal conductivity) and wear resistance that Iron 0.10 max bon, or strip—to perform as an electric heating allows cast nickel-beryllium-carbon alloys 0.01–0.10 element, it must resist the flow of electricity. to be used for tooling for glass forming oper- 0.30 max Most of the common and alloys such 0.008 max ations Silicon 0.10 max as stainless steels do resist the flow of electric- Titanium 0.005 max ity. The measure of this characteristic is re- These and other special-purpose alloys and ap- Nickel 99.00 min ferred to as “electrical resistivity.” It is ex- plications are described subsequently. pressed as either ohm millimeter square per meter (Ω⋅mm2/m) in metric units or ohm residual-element levels: times circular mils per foot (Ω⋅circular mil/ft) This grade is especially suitable for active cath- in English units. odes, vacuum tube anodes, and structural parts If resistivity alone was the prime factor for Commercially Pure Nickel of tubes. for Electronic Applications an electric heating element, the choice could be Nickel 270 (UNS N02270), a high-purity, from many alloy candidates in a broad spec- powder-produced nickel, is 99.97% nickel with trum of cost. However, there are a number of Commercially pure nickel is available in sev- a 0.001% maximum limit on cobalt, magne- requirements a material must meet in order to eral grades, slightly different in composition, to sium, chromium, titanium, sulfur, silicon, man- avoid failure and provide an extended service © 2000 ASM International. All Rights Reserved. www.asminternational.org ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys (#06178G) Special-Purpose Nickel Alloys / 93

Table 1 Typical properties of resistance heating materials

Average change in Thermal expansion, Resistivity(a), resistance(c), %, from 20 °C to: µm · °C, from 20 °C to: Tensile strength Basic composition Ω ·mm2 /m(b) 260 °C 540 °C 815 °C 1095 °C 100 °C 540 °C 815 °C MPa ksi g/cm3 lb/in.3 Nickel-chromium and nickel-chromium-iron alloys 78.5Ni-20Cr-1.5Si (80–20) 1.080 4.5 7.0 6.3 7.6 13.5 15.1 17.6 655–1380 95–200 8.41 0.30 77.5Ni-20Cr-1.5Si-1Nb 1.080 4.6 7.0 6.4 7.8 13.5 15.1 17.6 655–1380 95–200 8.41 0.30 68.5Ni-30Cr-1.5Si (70–30) 1.180 2.1 4.8 7.6 9.8 12.2 … … 825–1380 120–200 8.12 0.29 68Ni-20Cr-8.5Fe-2Si 1.165 3.9 6.7 6.0 7.1 … 12.6 … 895–1240 130–180 8.33 0.30 60Ni-16Cr-22Fe-1.5Si 1.120 3.6 6.5 7.6 10.2 13.5 15.1 17.6 655–1205 95–175 8.25 0.30 37Ni-21Cr-40Fe-2Si 1.08 7.0 15.0 20.0 23.0 14.4 16.5 18.6 585–1135 85–165 7.96 0.288 35Ni-20Cr-43Fe-1.5Si 1.00 8.0 15.4 20.6 23.5 15.7 15.7 … 550–1205 80–175 7.95 0.287 35Ni-20Cr-42.5Fe-1.5Si-1Nb 1.00 8.0 15.4 20.6 23.5 15.7 15.7 … 550–1205 80–175 7.95 0.287 Iron-chromium-aluminum alloys 83.5Fe-13Cr-3.25Al 1.120 7.0 15.5 … … 10.6 … … 620–1035 90–150 7.30 0.26 81Fe-14.5Cr-4.25Al 1.25 3.0 9.7 16.5 … 10.8 11.5 12.2 620–1170 90–170 7.28 0.26 73.5Fe-22Cr-4.5Al 1.35 0.3 2.9 4.3 4.9 10.8 12.6 13.1 620–1035 90–150 7.15 0.26 72.5Fe-22Cr-5.5Al 1.45 0.2 1.0 2.8 4.0 11.3 12.8 14.0 620–1035 90–150 7.10 0.26 Pure metals Molybdenum 0.052 110 238 366 508 4.8 5.8 … 690–2160 100–313 10.2 0.369 0.105 85 175 257 305 9.0 9.7 10.1 345 50 21.5 0.775 Tantalum 0.125 82 169 243 317 6.5 6.6 … 345–1240 50–180 16.6 0.600 0.055 91 244 396 550 4.3 4.6 4.6 3380–6480 490–940 19.3 0.697 Nonmetallic heating-element materials 0.995–1.995 –33 –33 –28 –13 4.7 … … 28 4 3.2 0.114 Molybdenum disilicide 0.370 105 222 375 523 9.2 … … 185 27 6.24 0.225 MoSi2 + 10% ceramic additives 0.270 167 370 597 853 13.1 14.2 14.8 … … 5.6 0.202 9.100 –16 –18 –13 –8 1.3 … … 1.8 0.26 1.6 0.057

(a) At 20 °C (68 °F). (b) To convert to Ω·circular mil/ft, multiply by 601.53. (c) Changes in resistance may vary somewhat, depending on cooling rate.

life. The primary requirements of materials Table 2 Recommended maximum furnace operating temperatures for resistance heating used for heating elements are high melting materials point, high electrical resistivity, reproducible temperature coefficient of resistance, good oxi- Approximate Maximum furnace dation resistance, absence of volatile compo- operating temperature in air nents, and resistance to . Other Basic composition, % °C °F °C °F desirable properties are good elevated-tempera- Nickel-chromium and nickel-chromium-iron alloys ture creep strength, high emissivity, low ther- 78.5Ni-20Cr-1.5Si (80–20) 1400 2550 1150 2100 mal expansion, and low modulus (both of 77.5Ni-20Cr-1.5Si-1Nb 1390 2540 68.5Ni-30Cr-1.5Si (70–30) 1380 2520 1200 2200 which help minimize thermal fatigue), good re- 68Ni-20Cr-8.5Fe-2Si 1390 2540 1150 2100 sistance to thermal shock, and good strength 60Ni-16Cr-22Fe-1.5Si 1350 2460 1000 1850 and ductility at fabrication temperatures. 35Ni-30Cr-33.5Fe-1.5Si 1400 2550 Property Data. Four groups of materials are 35Ni-20Cr-43Fe-1.5Si 1380 2515 925 1700 35Ni-20Cr-42.5Fe-1.5Si-1Nb 1380 2515 commonly used for high-temperature resistance heating elements: (1) nickel-chromium (Ni-Cr) Iron-chromium-aluminum alloys and nickel-chromium-iron (Ni-Cr-Fe) alloys, 83.5Fe-13Cr-3.25Al 1510 2750 1050 1920 81Fe-14.5Cr-4.25Al 1510 2750 (2) iron-chromium-aluminum alloys, (3) refrac- 79.5Fe-15Cr-5.2Al 1510 2750 1260 2300 tory metals, and (4) nonmetallic (ceramic) ma- 73.5Fe-22Cr-4.5Al 1510 2750 1280 2335 terials. Of these four groups, the Ni-Cr and 72.5Fe-22Cr-5.5Al 1510 2750 1375 2505 Ni-Cr-Fe alloys serve by far the greatest num- Pure metals ber of applications. Table 1 compares the phys- Molybdenum 2610 4730 400(a) 750(a) ical and mechanical properties of the four Platinum 1770 3216 1500 2750 Tantalum 3000 5400 500(a) 930(a) groups. Maximum operating temperatures for Tungsten 3400 6150 300(a) 570(a) resistance heating materials for furnace appli- Nonmetallic heating-element materials cations are given in Table 2. Additional prop- Silicon carbide 2410 4370 1600 2900 erty data on some of the Ni-Cr and Ni-Cr-Fe al- Molybdenum disilicide (b) (b) 1700–1800 3100–3270 loys listed in Tables 1 and 2 can be found in MoSi2 + 10% ceramic additives (b) (b) 1900 3450 data sheets published in the section Properties Graphite 3650–3700(b) 6610–6690(c) 400(d) 750(d) of Electrical Resistance Alloys in the article Recommended temperatures “Electrical Resistance Alloys” in Properties Element Vacuum Pure H2 gas and Selection: Nonferrous Alloys and Special- Mo 1650 °C (3000 °F) 1760 °C (3200 °F) 1700 °C (3100 °F) Purpose Materials, Volume 2 of the ASM Ta 2480 °C (4500 °F) Not recommended Not recommended Handbook. W 1650 °C (3000 °F) 2480 °C (4500 °F) 1700 °C (3100 °F) The resistivities of Ni-Cr and Ni-Cr-Fe al- (a) Recommended atmospheres for these metals are a vacuum of 10–4 to 10–5 mm Hg, pure hydrogen, and partly combusted city gas dried to a dew loys are high, ranging from 1000 to 1187 point of 4 °C (40 °F). In these atmospheres, the recommended temperatures, would be as shown above. (b) Decomposes before melting at approxi- Ω⋅ Ω⋅ mately 1740 °C (3165 °F) for MoSi2, and 1825 °C (3315 °F) for MoSi2 + 10% ceramic additives. (c) Graphite volatilizes without melting at 3650 to n m (600 to 714 circular mil/ft) at 25 °C. 3700 °C (6610 to 6690 °F). (d) At approximately 400 °C (750 °F) (threshold oxidation temperature), graphite undergoes a weight loss of 1% in 24 h Figure 1 shows that the resistance changes in air. Graphite elements can be operated at surface temperatures up to 2205 °C (4000 °F) in inert atmospheres. more rapidly with temperature for 35Ni-20Cr- © 2000 ASM International. All Rights Reserved. www.asminternational.org ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys (#06178G) 94 / Introduction to Nickel and Nickel Alloys

45Fe than for any other alloy in this . The Nickel Alloys for Resistors and Thermo- Table 3 presents base compositions, melting curve for 35Ni-30Cr-35Fe (which is no longer stats. In addition to their use as heating ele- points, and electrical resistivities of the eight produced) is similar but slightly lower. The ments in furnaces and appliances, nickel elec- standard . As indicated in the ta- other four curves, which are for alloys with trical resistance alloys are also used in ble, nickel-copper, nickel-chromium, nickel- substantially higher nickel contents, reflect rel- instruments and control equipment to measure silicon, and nickel alloys containing various atively low changes in resistance with tempera- and regulate electrical characteristics, for ex- combinations of aluminum, manganese, iron, ture. For these alloys, rate of change reaches a ample, resistors, and in applications where silicon, and cobalt are used as either the positive peak near 540 °C (1000 °F), goes through a heat generated in a metal resistor is converted (P) or negative (N) thermoelement. The maxi- minimum at about 760 to 870 °C (1400 to to mechanical energy, for example, thermostat mum operating temperatures and limiting envi- 1600 °F), and then increases again. For Ni-Cr metals. Resistor alloys include Ni-Cr and ronmental factors for these alloys are also listed alloys, the change in resistance with tempera- Ni-Cr-Fe alloys similar to those used for heat- in Table 3. A nonstandard nickel-base thermo- ture depends on section size and cooling rate. ing elements and 75Ni-20Cr-3Al alloys con- couple element consisting of 82Ni-18Mo alloy as Figure 2 presents values for a typical taining small amounts of other metals—usu- the positive themoelement and 99Ni-1Co alloy 80Ni-20Cr alloy. The maximum change (curve ally either copper, manganese, or iron. A as the negative thermoelement is also used in A) occurs with small sections, which cool rap- thermostat metal is a (usu- hydrogen or reducing atmospheres. More de- idly from the last production heat treatment. ally in the form of sheet or strip) that consists tailed information on devices and The smallest change occurs for heavy sections, of two or more materials bonded together, of materials can be found in the article “Thermo- which cool slowly. The average curve (curve which one may be a . Nickel-iron, couple Materials” in Properties and Selection: B) is characteristic of medium-size sections. nickel-chromium-iron, and nickel-copper al- Nonferrous Alloys and Special-Purpose Mate- loys are commonly used. Additional informa- rials, Volume 2 of the ASM Handbook and in tion on resistor and thermostat alloys can be “Thermocouple Materials” in the Metals Hand- found in the article “Electrical Resistance Al- book Desk Edition, Second Edition. loys” in Properties and Selection: Nonferrous Alloys and Special-Purpose Materials, Vol- ume 2 of the ASM Handbook. Nickel-Iron Soft Magnetic Alloys

Thermocouple Alloys Soft magnetic nickel-iron alloys containing from about 30 to 80% Ni are used extensively in applications requiring the following charac- The thermocouple thermometer is one of the teristics: most widely used devices for measurement of temperature in the metals industry. Essentially, • High permeability a thermocouple thermometer is a system con- • High sisting of a temperature-sensing element called • Low hysteresis-energy loss a thermocouple, which produces an electromo- • Low eddy-current loss in alternating flux tive force (emf) that varies with temperature, a • Low Curie temperature device for sensing emf, which may include a • Constant permeability with changing tem- printed scale for converting emf to equivalent perature temperature units, and an electrical conductor Fig. 1 Variation of resistance with temperature for six (extension ) for connecting the thermo- As shown in Table 4, these include electromag- Ni-Cr and Ni-Cr-Fe alloys. To calculate resis- couple to the sensing device. Although any netic and radio frequency shields, transform- tance at temperature, multiply resistance at room tempera- combination of two dissimilar metals and/or ers, amplifiers, tape recording head laminations, ture by the temperature factor. alloys will generate a thermal emf, only eight ground fault interrupter cores, antishoplifting de- thermocouples are in common industrial use vices, torque motors, and so on. today. These eight have been chosen on the basis The nickel-iron alloys are generally manu- of such factors as mechanical and chemical factured as strip or sheet product; however, bil- properties, stability of emf, reproducibility, and let, bar, and wire can be produced as needed. cost. Strip products are usually supplied in a

Table 3 Properties of standard thermocouples

Base Melting point, Resistivity, Recommended Max temperature Type Thermoelements composition °C nΩ ·m service °C °F J JP Fe 1450 100 Oxidizing or reducing 760 1400 JN 44Ni-55Cu 1210 500 K KP 90Ni-9Cr 1350 700 Oxidizing 1260 2300 KN 94Ni-Al, Mn, Fe, Si, Co 1400 320 N NP 84Ni-14Cr-1.4Si 1410 930 Oxidizing 1260 2300 NN 95Ni-4.4Si-0.15 Mg 1400 370 T TP OFHC Cu 1083 17 Oxidizing or reducing 370 700 TN 44Ni-55Cu 1210 500 E EP 90Ni-9Cr 1350 700 Oxidizing 870 1600 Fig. 2 Variation of resistance with temperature for EN 44Ni-55Cu 1210 500 80Ni-20Cr heating alloy. Curve A is for a speci- R RP 87Pt-13Rh 1860 196 Oxidizing or inert 1480 2700 men cooled rapidly after the last production heat treat- RN Pt 1769 104 ment. Curve C is for a specimen cooled slowly after the S SP 90Pt-10Rh 1850 189 Oxidizing or inert 1480 2700 last production heat treatment. Curve B represents the av- SN Pt 1769 104 erage value for material as delivered by the producer. To B BP 70Pt-30Rh 1927 190 Oxidizing, vacuum or inert 1700 3100 calculate resistance at temperature, multiply the resistance BN 94Pt-6Rh 1826 175 at room temperature by the temperature factor. © 2000 ASM International. All Rights Reserved. www.asminternational.org ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys (#06178G) Special-Purpose Nickel Alloys / 95 cold-rolled condition for stamping laminations melting practices are both used to produce tion melting (VIM). Figure 6 shows a historical or as thin foil for winding of tape toroidal low-nickel alloys, but nearly all of the high- perspective of the change in initial permeability cores. Strip and sheet products may also be nickel alloys are produced by vacuum induc- of 80Ni-4Mo-Fe alloys when VIM became supplied in a low-temperature, mill-annealed, fine-grain condition suitable for forming and deep drawing. Table 4 Applications for nickel-iron magnetically soft alloys

Specialty Special Application alloy property Classes of Commercial Alloys Instrument transformer 79Ni-4Mo-Fe, 77Ni-5Cu-2Cr-Fe, 49Ni-Fe High permeability, low noise and losses Audio transformer 79Ni-4Mo-Fe, 49Ni-Fe, 45Ni-Fe, High permeability, low noise and losses, 45Ni-3Mo-Fe transformer grade Two broad classes of commercial alloys Hearing aid transformers 79Ni-4Mo-Fe High initial permeability, low losses have been developed in the nickel-iron system. Radar pulse transformers Oriented 49Ni-Fe, 79Ni-4Mo-Fe, Processed for square hysteresis loop, tape Based on nickel content, these include high- 45Ni-3Mo-Fe toroidal cores nickel alloys (about 79% Ni) and low-nickel al- Magnetic amplifiers Oriented 49Ni-Fe, 79Ni-4Mo-Fe Processed for square hysteresis loop, tape toroidal cores loys (about 45 to 50% Ni). Some alloys con- Transducers 45-50Ni-Fe High saturation magnetostriction taining even lower nickel contents (~29 to Shielding 79Ni-4Mo-Fe, 77Ni-5Cu-2Cr-Fe, High permeability at low induction levels 36%) can be used for measuring instruments re- 49Ni-Fe quiring magnetic temperature compensation Ground fault (GFI) interruptor core 79Ni-4Mo-Fe High permeability, temperature stability Sensitive direct current relays 45 to 49Ni-Fe, 78.5Ni-Fe High permeability, low losses, low coercive (see Table 4). force The effect of nickel content in nickel-iron al- Tape recorder head laminations 79Ni-5Mo-Fe High permeability, low losses (0.05 to 0.03 mm, loys on saturation induction (Bs) and on initial or 0.002 to 0.001 in.) µ Temperature compensator 29 to 36Ni-Fe Low Curie temperature permeability ( o) after annealing are illustrated Dry reed magnetic switches 51Ni-Fe Controlled expansion glass/metal sealing in Fig. 3 and 4. Below ~28% Ni, the crystal- Chart recorder (instrument) motors, 49Ni-Fe Moderate saturation, low losses, nonoriented line structure is body-centered cubic (bcc) synchronous motors grade low-carbon martensite if cooled rapidly and Loading coils 81-2 brittle Moly- Constant permeability with changing temperature and if cooled slowly, and these alloys are not considered useful for soft magnetic applications. Above ~28% Ni, the structure is face-centered cubic (fcc) austenite. The Curie temperature in this system is approx- imately room temperature at ~28% Ni and in- creases rapidly up to ~610 °C (1130 °F) at 68% Ni. Thus, these austenitic alloys are ferromag- netic. The high-nickel alloys containing about 79% Ni have high initial and maximum permeabilities (Fig. 4) and very low hysteresis losses, but they also have a saturation induction of only about 0.8 T (8 kG) as shown in Fig. 3. Alloying additions of 4 to 5% Mo, or of copper and chromium to 79Ni-Fe alloys, serve to ac- centuate particular magnetic characteristics. Popular high-permeability alloys include the MolyPermalloys (typically 80Ni-4 to 5Mo-bal Fe) and MuMetals (typically 77Ni-5Cu-2Cr-bal Fe). The magnetic properties of high-nickel al- loys are very dependent on processing and heat treatment. Figure 5 illustrates that in ~78.5Ni- Fe, the initial permeability was low after either furnace cooling or baking at 450 °C (840 °F). However, if the same alloy was rapidly cooled from 600 °C (1110 °F), the initial permeability was increased dramatically. High-purity 78.5Ni- Fe can exhibit an initial direct current (dc) per- meability of 5 × 104 and a maximum perme- ability of 3 × 105. These properties are obtained on ring laminations annealed in dry hydrogen at 1175 °C (2150 °F), rapid furnace cooled to room temperature, then reheated to 600 °C (1110 °F), and oil quenched. This alloy has lim- ited commercial use because the complex heat treatment is not easily performed on parts. Also, its electrical resistivity is only 16 µΩ ⋅ cm, which allows large eddy-current losses in alter- nating current (ac) applications. High-permeability alloys must also be of Fig. 3 Magnetic saturation of binary nickel-iron alloys at various field strengths. All samples were annealed at 1000 °C high commercial purity. Air-melting and vacuum- (1830 °F) and cooled in the furnace. © 2000 ASM International. All Rights Reserved. www.asminternational.org ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys (#06178G) 96 / Introduction to Nickel and Nickel Alloys widely used around 1960. Interstitial impurities temperature range. The rate of cooling through maximum permeability than the 79% Ni alloys such as carbon, sulfur, oxygen, and nitrogen the ordering range is typically 55 to 350 °C/h (Fig. 4), but the low-nickel alloys have a higher must be minimized by special melting proce- (100 to 630 °F/h), depending on the alloy being saturation induction (about 1.5 T, or 15 kG, as dures and by careful final annealing of lamina- heat treated. Although the cooling rate below shown in Fig. 3). Values of initial permeability tions and other core configurations. Sulfur con- the ordering range is not critical, stresses due to (at a magnetic induction, B, or 4 mT, or 40 G) tents higher than several ppm and carbon in ex- rapid quenching must be avoided. above 1.2 × 104 are typically obtained in low- cess of 20 ppm are detrimental to final-annealed Vacuum furnaces may be used to anneal nickel alloys, and values above 6 × 104 are magnetic properties in high-nickel alloys. some high-nickel soft magnetic alloys if the ap- typically obtained for 79Ni-4Mo-Fe alloys at Laminations or parts made from these high- plication does not demand the optimum mag- 60 Hz using 0.36 mm (0.014 in.) thick lamina- nickel alloys are usually commercially an- netic properties. However, dry hydrogen is tions. nealed in pure dry hydrogen (dew point less strongly recommended for annealing nickel- In alloys containing approximately 45 to than –50 °C, or –58 °F, at ~1000 to 1205 °C, or iron alloys. Parts must always be thoroughly 50% Ni, the effect of cooling rate on initial per- 1830 to 2200 °F) for several hours to eliminate degreased to remove oils (particularly sul- meability is not great, as evidenced in Fig. 5. stresses, to increase grain size, and to provide fur-bearing oils) prior to annealing. The typical annealing cycle to develop high for alloy purification. They are cooled at any The low-nickel alloys containing approxi- permeability for these low-nickel alloys is simi- practical rate down to the critical ordering mately 45 to 50% Ni are lower in initial and lar to the high-nickel cycle, except that any cooling rate between ~55 °C/h (100 °F/h) and ~140 °C/h (252 °F/h) is usually suggested. A dry hydrogen atmosphere is also recommended for annealing low-nickel alloys. Property Data. The magnetic properties of the nickel-iron soft magnetic alloys are a func- tion of strip thickness, melting procedure, chemical analysis, and freedom from contami- nants such as carbon, sulfur, and oxygen that can be picked up during melting, machining, or annealing. As described earlier, these alloys must be annealed in an inert dry hydrogen at- mosphere to reduce carbon, to prevent surface oxidation during the annealing cycle, and to promote optimum magnetic properties. Tables 5 and 6 provide typical dc and ac magnetic characteristics of nickel-iron alloys. Table 7 lists recommended heat treatments and the re- sulting mechanical properties.

Low-Expansion Alloys

The room-temperature coefficients of ther- mal expansion for most metals and alloys range

Fig. 5 Relative initial permeability at 2 mT (20 G) for Ni-Fe alloys given various heat treatments. Treat- ments were as follows: furnace cooled—1 h at 900 to 950 °C (1650 to 1740 °F), cooled at 100 °C/h (180 °F/h); baked—furnace cooled plus 20 h at 450 °C (840 °F); dou- ble treatment—furnace cooled plus 1 h at 600 °C (1110 °F) Fig. 4 Effect of nickel content on initial permeability, Curie temperature, and transformation in nickel-iron alloys and cooled at 1500 °C/min (2700 °F/min). © 2000 ASM International. All Rights Reserved. www.asminternational.org ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys (#06178G) Special-Purpose Nickel Alloys / 97 from about 5 to 25 µm/m ⋅ K. For some appli- • Components for radios and other electronic ate expansion characteristics can be selected. cations, however, alloys must be selected that devices The alloy containing 36% nickel (with small exhibit a very low thermal expansion (0 to 2 • Structural components in optical and laser quantities of manganese, silicon, and carbon µm/m ⋅ K) or display uniform and predictable measuring systems amounting to a total of less than 1%) has a co- expansion over certain temperature ranges. efficient of expansion so low that its length is This has resulted in a family of iron-nickel, Low-expansion alloys are also used with high- almost invariable for ordinary changes in tem- iron-nickel-chromium, and iron-nickel-cobalt expansion alloys (65%Fe-27%Ni-5%Mo, perature. This alloy is known as , meaning low-expansion alloys used in applications such or 53%Fe-42%Ni-5%Mo) to produce move- invariable. as the following: ments in thermoswitches and other temperature- After the discovery of Invar, an intensive regulating devices. study was made of the thermal and elastic prop- • Rods and tapes for geodetic surveying erties of several similar alloys. Iron-nickel al- • Compensating and balance wheels loys that have nickel contents higher than that for clocks and watches Effect of Nickel on the of Invar retain to some extent the expansion • Moving parts that require control of expan- Thermal Expansion of Iron characteristics of Invar. Alloys that contain less sion, such as pistons for some internal- than 36% nickel have much higher coefficients combustion engines Nickel has a profound effect on the thermal of expansion than alloys containing 36% or • Bimetal strip expansion of iron. Depending on the nickel more nickel. • Glass-to-metal seals content, alloys of iron and nickel have coeffi- • Thermostatic strip cients of linear expansion ranging from a small • Vessels and piping for storage and transpor- negative value (–0.5 µm/m ⋅ K) to a large posi- Invar (Fe-36%Ni Alloy) tation of tive value (20 µm/m ⋅ K). Figure 7 shows the • Superconducting systems in power transmis- effect of nickel content on the linear expansion sions of iron-nickel alloys at room temperature. In Invar (UNS number K93601) and related bi- • Integrated-circuit lead frames the range of 30 to 60% Ni, alloys with appropri- nary iron-nickel alloys have low coefficients of expansion over only a rather narrow range of temperature (see Fig. 8). At low temperatures in the region from A to B, the coefficient of ex- pansion is high. In the interval between B and C, the coefficient decreases, reaching a mini- mum in the region from C to D. With increas- ing temperature, the coefficient begins again to increase from D to E, and thereafter (from E to F), the expansion curve follows a trend similar to that of the nickel or iron of which the alloy is composed. The minimum expansivity prevails only in the range from C to D. In the region between D and E in Fig. 8, the coefficient is changing rapidly to a higher value. The temperature limits for a well-annealed 36% Ni iron are 162 and 271 °C (324 and 520 °F). These temperatures correspond to the initial and final losses of in the material (that is, the Curie temperature). The slope of the curve between C and D is, then, a measure of the coefficient of expansion over a limited range of temperature. Table 8 gives coefficients of linear expan- Fig. 6 Progress in initial permeability values of commercial-grade nickel-iron alloys since early 1940s. Frequency, f, is sion of iron-nickel alloys between 0 and 38 °C 60 Hz. Thickness of annealed laminations was 0.36 mm (0.014 in.). (32 and 100 °F). The expansion behavior of

Table 5 Typical direct current magnetic properties of annealed high-permeability nickel-iron alloys Data for 0.30 to 1.52 mm (0.012 to 0.060 in.) thickness strip; ring laminations annealed in dry hydrogen at 1175 °C (2150 °F) (unless otherwise noted), 2 to4hattemperature. ASTM A 596

Permeability Approximate induction at Saturation, µ Maximum, maximum permeability, m Residual induction Br Coercive force, Hc induction, (Bs) Resistivity, 3 µ 3 –1 µΩ Alloy Initial × 10 m ×10 T kG T kG A·m Oe T kG ·cm Low nickel 45Ni-Fe 7(a) 90 0.6 6 0.68 6.8 4 0.05 1.58 15.8 50 49Ni-Fe(b) 6.1(a) 64 0.8 8 0.96 9.6 8 0.10 1.55 15.5 47 49Ni-Fe(c) 14(a) 140 0.78 7.8 0.97 9.7 4 0.05 1.55 15.5 47 49Ni-Fe 17(a) 180 0.75 7.5 0.90 9.0 2.4 0.03 1.55 15.5 47 45Ni-3Mo-Fe 6(a) 60 0.62 6.2 0.89 8.9 4.8 0.06 1.45 14.5 65 High nickel 78.5Ni-Fe 50(d) 300 0.35 3.5 0.50 5.0 1.0 0.013 1.05 10.5 16 79Ni-4Mo-Fe 90(d) 400 0.28 2.8 0.35 3.5 0.3 0.004 0.79 7.9 59 75Ni-5Cu-2Cr-Fe 85(d) 375 0.25 2.5 0.34 3.4 0.4 0.005 0.77 7.7 56

(a) Measured at B = 10 mT (100 G). (b) Annealed at 955 °C (1750 °F). (c) Annealed at 1065 °C (1950 °F). (d) Measured at B = 4 mT (40 G) © 2000 ASM International. All Rights Reserved. www.asminternational.org ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys (#06178G) 98 / Introduction to Nickel and Nickel Alloys several iron-nickel alloys over wider ranges of considerable influences on the position of this icantly changes thermal expansion characteris- temperature is represented by curves 1 to 5 in minimum. Because further additions of nickel tics. Minimum expansivity shifts toward higher Fig. 9. For comparison, Fig. 9 also includes the raise the temperature at which the inherent nickel contents when manganese or chromium similar expansion obtained for ordinary . magnetism of the alloy disappears, the inflec- is added and toward lower nickel contents Effects of Composition on Expansion Co- tion temperature in the expansion curve (Fig. 8) when copper, cobalt, or carbon is added. Ex- efficient. Figure 7 shows the effect of variation also rises with increasing nickel content. cept for the ternary alloys with Ni-Fe-Co com- in nickel content on linear expansivity. Mini- The addition of third and fourth elements to positions, the value of the minimum expan- mum expansivity occurs at approximately 36% iron-nickel provides useful changes of desired sivity for any of these ternary alloys is, in Ni, and small additions of other metals have properties (mechanical and physical) but signif- general, greater than that of a typical Invar al- loy. Figure 10 shows the effects of additions of Table 6 Typical alternating current magnetic properties of annealed high-permeability manganese, chromium, copper, and carbon. nickel-iron alloys Additions of silicon, tungsten, and molybde- num produce effects similar to those caused by Impedance permeability, µ ×103, at indicated induction, B(a) Nominal Thickness, Cyclic z additions of manganese and chromium; the composition mm (in.) frequency, Hz B =4mT(40G) B = 20 mT (200 G) B = 0.2 T (2 kG) B = 0.4 T (4 kG) B = 0.8 T (8 kG) composition of minimum expansivity shifts to- 49Ni-Fe(b) 0.51 (0.020) 60 10.2 16.5 31.3 40.1 ... ward higher contents of nickel. Addition of car- 0.36 (0.014) 60 12 19.4 37.3 48.2 54.7 bon is said to produce instability in Invar, 0.25 (0.010) 60 12 20.5 42.5 54.9 68.9 0.15 (0.006) 60 12 21 47 63.5 85.3 which is attributed to the changing solubility of 0.51 (0.020) 400 4.7 5.9 11.7 11.3 ... carbon in the austenitic matrix during heat 0.36 (0.014) 400 6.1 7.9 14.4 17.7 13.3 treatment. 0.15 (0.006) 400 8.8 12.6 21.8 28.6 35 Effects of Processing. Heat treatment and 79Ni-4Mo-Fe 0.36 (0.014) 60 68 77 100 ...... cold work change the expansivity of Invar al- 79Ni-5Mo-Fe 0.15 (0.006) 60 90 110 170 ...... 0.10 (0.004) 60 110 135 230 ...... loys considerably. Table 9 shows the effect of 0.03 (0.001) 60 100 120 180 ...... heat treatment for a 36% Ni Invar alloy. The 0.36 (0.014) 400 23.2 25.4 30.5 ...... expansivity is greatest in well-annealed mate- 0.15 (0.006) 400 49.7 52.4 64.5 ...... rial and least in quenched material. 0.03 (0.001) 400 89.6 105.2 180.4 ...... Annealing is done at 750 to 850 °C (1380 to 49Ni-Fe(c) 0.36 (0.014) 60 ...... 0.15 (0.006) 60 ...... 1560 °F). When the alloy is quenched in water 0.36 (0.014) 400 ...... from these temperatures, expansivity is de- 0.15 (0.006) 400 ...... creased, but instability is induced both in actual µ 3 Inductance permeability, L ×10 , DU laminations(d) length and in coefficient of expansion. To over- Nominal composition B = 4 mT( 40 G) B = 20 mT (200 G) B = 0.2 T (2 kG) B = 0.4 T (4 kG) B = 0.8 T (8 kG) come these deficiencies and to stabilize the ma- 49Ni-Fe(b) ...... terial, it is common practice to stress relieve at ...... approximately 315 to 425 °C (600 to 800 °F) ...... and to age at a low temperature 90 °C (200 °F) ...... for 24 to 48 hours...... Cold drawing also decreases the thermal ex- 79Ni-4Mo-Fe ...... pansion coefficient of Invar alloys. The values 79Ni-5Mo-Fe ...... for the coefficients in the following table are ...... from experiments on two heats of Invar: ...... Material condition Expansivity, ppm/°C ...... Direct from hot mill 1.4 (heat 1) ...... 1.4 (heat 2) 49Ni-Fe(c) 18.6 35.8 78 110 135 Annealed and quenched 0.5 (heat 1) 19.6 39.2 98.5 142 215 0.8 (heat 2) 11.8 17.6 36.4 55 30 Quenched and cold drawn (>70% 0.14 (heat 1) 12.2 18.5 48.3 95 164 reduction with a diameter of 3.2 to 0.3 (heat 2) Core loss in mW/kg (mW/lb) at indicated induction B 6.4 mm, or 0.125 to 0.250 in.) Nominal composition B =4mT(40G) B = 20 mT (200 G) B = 0.2 T (2 kG) B = 0.4 T (4 kG) B = 0.8 T (8 kG) By cold working after quenching, it is possi- 49Ni-Fe(b) ...... ble to produce material with a zero, or even a 0.011 (0.005) 0.21 (0.097) 15 (6.7) 48 (21.7) 160 (73) ...... negative, coefficient of expansion. A negative 0.009 (0.004) 0.21 (0.094) 13 (5.8) 44 (19.9) 135 (62) coefficient can be increased to zero by careful ...... annealing at a low temperature. 0.21 (0.094) 4.34 (1.97) 282 (128) 905 (410) 3880 (1760) Magnetic Properties. Invar and all similar 0.15 (0.069) 3.20 (1.45) 238 (108) 705 (320) 2310 (1050) 79Ni-4Mo-Fe ... 0.099 (0.045) 6.50 (2.95) ...... iron-nickel alloys are ferromagnetic at room 79Ni-5Mo-Fe ... 0.051 (0.023) 3.00 (1.36) ...... temperature and become paramagnetic at ... 0.024 (0.011) 1.60 (0.73) ... higher temperatures. Because additions in ...... nickel content raise the temperature at which 0.11 (0.050) 2.20 (1.00) 160 (72.5) ...... 0.044 (0.020) 0.99 (0.45) 65.9 (29.9) ...... the inherent magnetism of the alloy disappears, ...... the inflection temperature in the expansion 49Ni-Fe(c) 0.011 (0.005) 0.22 (0.10) 15 (6.6) 51 (23) 185 (83) curve rises with increasing nickel content. The 0.007 (0.003) 0.13 (0.06) 8.6 (3.9) 31 (14) 105 (47) loss of magnetism in a well-annealed sample of 0.20 (0.091) 4.4 (2.00) 306 (139) 1010 (460) 4800 (2200) 0.11 (0.052) 2.38 (1.08) 172 (78.0) 550 (250) 1700 (790) a true Invar begins at 162 °C (324 °F) and ends at 271 °C (520 ° F). In a quenched sample, the (a) Tested per ASTM A 772 method: thicknesses >0.13 mm (0.005 in.) tested using ring specimens; <0.13 mm (0.005 in.) tested via tape toroid speci- loss begins at 205 °C (400 °F) and ends at mens. (b) Nonoriented rotor or motor grade. (c) Transformer semioriented grade. (d) Per ASTM A 346 method; DU, interleaved U-shape transformer 271 °C (520 °F). © 2000 ASM International. All Rights Reserved. www.asminternational.org ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys (#06178G) Special-Purpose Nickel Alloys / 99

Table 7 Typical heat treatments and physical properties of nickel-iron alloys Table 8 Thermal expansion of iron-nickel alloys between 0 and 38 °C Ultimate µ Alloy nominal ASTM Annealing Strength tensile strength Elongation, Specific Ni, % Mean coefficient, m/m·K composition standard treatment(a) Hardness MPa ksi MPa ksi % gravity 31.4 3.395 + 0.00885 t 45Ni-Fe A 753 Type 1 Dry hydrogen, 1120 to 48 HRB 165 24 441 64 35 8.17 34.6 1.373 + 0.00237 t 1175 °C (2050 to 2150 °F), 35.6 0.877 + 0.00127 t 2 to 4 h, cool at nominally 37.3 3.457 – 0.00647 t 85 °C/h (150 °F/h) 39.4 5.357 – 0.00448 t 49Ni-Fe A 753 type 2 Same as 45Ni-Fe 48 HRB 165 24 441 64 35 8.25 43.6 7.992 – 0.00273 t 45Ni-3Mo-Fe ... Same as 45Ni-Fe ...... 8.27 44.4 8.508 – 0.00251 t 78.5Ni-Fe ... Dry hydrogen, 1175 °C 50 HRB 159 23 455 66 35 8.60 48.7 9.901 – 0.00067 t (2150 °F), 4 h rapid cool to 50.7 9.984 + 0.00243 t RT(b), reheat to 600 °C 53.2 10.045 + 0.00031 t (1110 °F), 1 h, oil quench to RT 80Ni-4Mo-Fe A 753 type 4 Dry hydrogen, 1120 to 1175 58 HRB 172 25 545 79 37 8.74 °C (2050 to 2150 °F), 2 to 4 Table 9 Effect of heat treatment on h cool through critical coefficient of thermal expansion of Invar ordering temperature range, ~760 to400 °C Condition Mean coefficient, µm/m·K (1400 to 750 °F) at a rate specified for the particular As forged alloy, typically 55 °C/h At 17–100 °C (63–212 °F) 1.66 (100 °F/ h) up to ~390 °C/h At 17–250 °C (63–480 °F) 3.11 (700 °F/h) 80Ni-5Mo-Fe A 753 type 4 Same as 80Ni-4Mo-Fe 58 HRB 172 25 545 79 37 8.75 Quenched from 830 °C (1530 °F) 77Ni-5Cu-2Cr-Fe A 753 type 3 Same as 80Ni-4Mo-Fe 50 HRB 125 18 441 64 27 8.50 At 18–100 °C (65–212 °F) 0.64 At 18–250 °C (65–480 °F) 2.53 (a) All nickel-iron soft magnetic alloys should be annealed in a dry (–50 °C, or –58 °F) hydrogen atmosphere, typically for 2 to 4 h; cool as recom- mended by producer. Vacuum annealing generally provides lower properties, which may be acceptable depending upon specific application. (b) RT, Quenched from 830 °C and tempered room temperature At 16–100 °C (60–212 °F) 1.02 At 16–250 °C (60–480 °F) 2.43 Quenched from 830 °C to room temperature in 19 h At 16–100 °C (60–212 °F) 2.01 At 16–250 °C (60–480 °F) 2.89

Fig. 8 Change in length of a typical Invar alloy over dif- ferent ranges of temperature Fig. 7 Coefficient of linear expansion at 20 °C versus Ni content for Fe-Ni alloys containing 0.4% Mn and 0.1% C 6 Mn

4

2 Cr

0 Change in % Ni –2 Cu C –4 (a) 8 6 Mn 6 Cr

4 Cu C 2

Increase in coefficient × 10 0 0 1 2 3 4 5 6 7 8 9 10

(b) Alloying element, % Fig. 9 Thermal expansion of iron-nickel alloys. Curve 1, 64Fe-31Ni-5Co; curve 2, 64Fe-36Ni (Invar); Fig. 10 Effect of alloying elements on expansion characteristics of iron-nickel alloys. (a) Displacement of nickel con- curve 3, 58Fe-42Ni; curve 4, 53Fe-47Ni; curve 5, tent caused by additions of manganese, chromium, copper, and carbon to alloy of minimum expansivity. (b) 48Fe-52Ni; curve 6, (0.25% C) Change in value of minimum coefficient of expansion caused by additions of manganese, chromium, copper, and carbon © 2000 ASM International. All Rights Reserved. www.asminternational.org ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys (#06178G) 100 / Introduction to Nickel and Nickel Alloys

Electrical Properties. The electrical resis- netic characteristics with temperature change. mately 42 to 48% nickel with chromium of 4 to tance of 36Ni-Fe Invar is between 750 and 850 They are used as compensating shunts in meter- 6%. nΩ⋅m at ordinary temperatures. The tempera- ing devices and speedometers. ture coefficient of electrical resistivity is about Alloys Containing 42 to 50% Ni. Applica- 1.2 mΩ/Ω · K over the range of low expansivity. tions for these alloys include semiconductor Iron-Nickel-Cobalt Alloys As nickel content increases above 36%, the elec- packaging components, thermostat bimetals, glass- trical resistivity decreases to approximately 165 to-metal sealing, and glass sealing of fiber op- Super-Invar. Substitution of ~5% Co for nΩ⋅m at approximately 80% NiFe. tics. Typical compositions and thermal expan- some of the nickel content in the 36% Ni (In- Other Physical and Mechanical Prop- sion characteristics for some of these alloys are var) alloy provides an alloy with an expansion erties. Table 10 presents data on miscellaneous given in Table 11. Included in this group is coefficient even lower than Invar. A Super-In- properties of Invar in the hot-rolled and forged Dumet wire, an alloy containing 42% Ni that is var alloy with a nominal 32% Ni and 4 to 5% conditions. Figure 11 illustrates the effects of clad with copper to provide improved electrical Co will exhibit a thermal expansion coefficient temperature on mechanical properties of forged conductivity and to prevent gassing at glass close to zero, over a relatively narrow tempera- 66Fe-34Ni. seals. ture range. This alloy has been used as struc- tural components or bases for optical and laser instruments. Iron-Nickel Alloys Other Than Invar Iron-Nickel-Chromium Alloys (UNS K94610) is a nominal 29% Ni-17%Co-54%Fe alloy that is a well-known Alloys containing less than 36% Ni in- is a low-expansion iron-nickel-chro- glass-sealing alloy suitable for sealing to hard clude temperature compensator alloys (30 to mium alloy with a thermoelastic coefficient of (borosilicate) glasses. Kovar has a nominal ex- 34% Ni). These exhibit linear changes in mag- zero over a wide temperature range. It is more pansion coefficient of approximately 5 ppm/°C practical than the straight iron-nickel alloys and inflection temperature of ~450 °C (840 °F). with a zero thermoelastic coefficient because Kovar is widely used for making hermetic seals Table 10 Physical and mechanical its thermoelastic coefficient is less susceptible with the harder borosilicate (Pyrex, Corning, properties of Invar to variations in nickel content expected in com- Inc., Corning, NY) glass and ceramic materials mercial melting. used in power tubes, microwave tubes, transis- Solidus temperature, °C (°F) 1425 (2600) Elinvar is used for such articles as hair- tors, and diodes, as well as in integrated cir- Density, g/cm3 8.1 Tensile strength, MPa (ksi) 450–585 (65–85) springs and balance wheels for clocks and cuits. Yield strength, MPa (ksi) 275–415 (40–60) watches and for tuning forks used in radio syn- Elastic limit, MPa (ksi) 140–205 (20–30) chronization. Particularly beneficial where an Elongation, % 30–45 invariable modulus of elasticity is required, it Hardenable Low-Expansion, Reduction in area, % 55–70 Controlled-Expansion, and Scleroscope hardness 19 has the further advantage of being compara- Brinell hardness 160 tively rustproof. Constant-Modulus Alloys Modulus of elasticity, GPa (106 psi) 150 (21.4) The composition of Elinvar has been modi- µ Thermoelastic coefficient, m/m·K 500 fied somewhat from its original specification of Hardenable Low-Expansion/Constant-Modu- Specific heat, at 25–100 °C (78–212 °F), 515 (0.123) J/kg · °C (Btu/lb · °F) 36% Ni and 12% Cr. The limits now used are lus Alloys. Alloys that have low coefficients of , at 20–100 °C 11 (6.4) 33to35Ni,53to61Fe,4to5Cr,1to3W,0.5 expansion, and alloys with constant modulus of (68–212 °F), W/m · K (Btu/ft · h · °F) to 2 Mn, 0.5 to 2 Si, and 0.5 to 2 C. Elinvar, as elasticity, can be made age hardenable by add- Thermoelectric potential (against copper), 9.8 µ created by Guillaume and Chevenard, contains ing titanium. In low-expansion alloys, nickel con- at –96 °C (–140 °F), V/K 32% Ni, 10% Cr, 3.5% W, and 0.7% C. tent must be increased when titanium is added. Other iron-nickel-chromium alloys with The higher nickel content is required because any 40 to 48% Ni and 2 to 8% Cr are useful as titanium that has not combined with the carbon Temperature, ûF 200 400 600 800 1000 1200 1400 glass-sealing alloys because the chromium in the alloy will neutralize more than twice its 800 promotes improved glass-to-metal bonding as own weight in nickel by forming an intermetallic 100 a result of its -forming characteristics. compound during the hardening operation. The most common of these contain approxi- 600

400 60 Table 11 Composition and typical thermal expansion coefficients for common iron-nickel low-expansion alloys

200 Composition(a), % Tensile strength, ksi Tensile ASTM Tensile strength, MPa Tensile 20 Alloy specification C (max) Mn (max) Si (max) Ni (nom) 0 42 Ni-Iron F 30 0.02 0.5 0.25 41 0 200 400 600 800 46 Ni-Iron F 30 0.02 0.5 0.25 46 Temperature, ûC 48 Ni-Iron F 30 0.02 0.5 0.25 48 52 Ni-Iron F 30 0.02 0.5 0.25 51 Temperature, ûF 42 Ni-Iron (Dumet) F 29 0.05 1.0 0.25 42 200 400 600 800 1000 1200 1400 42 Ni-Iron (Thermostat) B 753 0.10 0.4 0.25 42 80 Typical thermal expansion coefficients from room temperature to: Reduction in area 300 °C (570 °F) 400 °C (750 °F) 500 °C (930 °F) 40 Alloy ppm/°C ppm/°F ppm/°C ppm/°F ppm/°C ppm/°F Elongation 42 Ni-Iron 4.4 2.4 6.0 3.3 7.9 4.4 Ductility, % Ductility, 46 Ni-Iron 7.5 4.2 7.5 4.2 8.5 4.7 0 0 200 400 600 800 48 Ni-Iron 8.8 4.9 8.7 4.8 9.4 5.2 Temperature, C 52 Ni-Iron 10.1 5.6 9.9 5.5 9.9 5.5 û 42 Ni-Iron (Dumet) ...... 6.6 3.7 ... … 42 Ni-Iron (Thermostat) 5.8(b) 3.2(b) 5.6(c) 3.1(c) 5.7(d) 3.15(d) Fig. 11 Mechanical properties of a forged 34% Ni al- loy. Alloy composition: 0.25 C, 0.55 Mn, 0.27 (a) Balance of iron with residual impurity limits of 0.25% max Si, 0.015% max P, 0.01% max S, 0.25% max Cr, and 0.5% max Co. (b) From room Si, 33.9 Ni, bal Fe. Heat treatment: annealed at 800 °C temperature to 90 °C (200 °F). (c) From room temperature to 150 °C (300 °F). (d) From room temperature to 370 °C (700 °F) (1475 °F) and furnace cooled © 2000 ASM International. All Rights Reserved. www.asminternational.org ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys (#06178G) Special-Purpose Nickel Alloys / 101

As shown in Table 12, addition of titanium mum expansion occurs. Titanium also lowers duration of aging varies from 48 h at 600 °C raises the lowest attainable rate of expansion the inflection temperature. Mechanical proper- (1110°F)to3hat730°C(1345°F)forsolution- and raises the nickel content at which the mini- ties of alloys containing 2.4% titanium and treated material. 0.06% carbon are given in Table 13. For material that has been solution treated In alloys of the constant-modulus type con- and subsequently cold worked 50%, aging time Table 12 Minimum coefficient of taining chromium, addition of titanium allows varies from4hat600°C(1100 °F) to1hat expansion in low-expansion Fe-Ni alloys the thermoelastic coefficients to be varied by 730 °C (1350 °F). Table 15 gives mechanical containing titanium adjustment of heat-treating schedules. The al- properties of a constant-modulus alloy contain-

Optimum Minimum coefficient loys in Table 14 are the three most widely ing 42% Ni, 5.4% Cr, and 2.4% Ti. Heat treat- Ti, % Ni, % of expansion, m m/m·K used compositions. The recommended solution ment and cold work markedly affect these 0 36.5 1.4 treatment for the alloys that contain 2.4% Ti is properties. 2 40.0 2.9 950 to 1000 °C (1740 to 1830 °F) for 20 to 90 High-strength controlled-expansion super- 3 42.5 3.6 min, depending on section size. Recommended alloys are based on the iron-nickel-cobalt sys- tem. They are strengthened by the addition of the age-hardening elements , titanium, Table 13 Mechanical properties of low-expansion Fe-Ni alloys containing 2.4 Ti and 0.06 C and aluminum. As indicated in Table 16, these alloys exhibit both a low and constant coeffi- Tensile strength Yield strength Elongation(a), Hardness, cient of expansion up to about 430 °C (800 °F). Condition MPa ksi MPa ksi % HB They also provide high strength at temperatures 42Ni-55.5Fe-2.4Ti-0.06C(b) up to 540 °C (1000 °F). These alloys have been Solution treated 620 90 275 40 32 140 used by the aerospace industry to design near Solution treated and age hardened 1140 165 825 120 14 330 net-shape components and to provide closer Solution treated, cold rolled 50% and 1345 195 1140 165 5 385 age hardened clearance between the tips of rotating turbine blades and retainer rings. This allows for 52Ni-45.5Fe-2.4Ti-0.06C(c) greater power output and fuel efficiencies. Solution treated 585 85 240 35 27 125 Solution treated and age hardened 825 120 655 95 17 305 These high-strength alloys also allow increased strength-to-weight ratios in engine design, re- (a) In 50 mm (2 in.). (b) Inflection temperature, 220 °C (430 °F); minimum coefficient of expansion, 3.2 m m/m ·K. (c) Inflection temperature, 440 °C sulting in weight savings. Alloy 909 (UNS (824 °F); minimum coefficient of expansion, 9.5 m m/m ·K N19909) offers attractive properties for rocket engine thrust chambers, ordnance hardware, Table 14 Thermoelastic coefficients of constant modulus Fe-Ni-Cr-Ti alloys springs, gage blocks, and instrumentation. Ad- ditional information on iron-nickel-cobalt con- Thermoelastic coefficient, Range of possible trolled expansion alloys can be found in the ar- Composition, % annealed condition, coefficients(a), ticle “Uses of Cobalt” in this Handbook. Ni Cr C Ti m m/m·K m m/m·K 42 5.4 0.06 2.4 0 18 to –23 42 6.0 0.06 2.4 36 54 to 13 42 6.3 0.06 2.4 –36 –18 to –60 Nickel-Titanium

(a) Any value in this range can be obtained by varying the heat treatment. Shape Memory Alloys

Metallic materials that demonstrate the abil- Table 15 Mechanical properties of constant-modulus alloy 50Fe-42Ni-5.4Cr-2.4Ti ity to return to some previously defined shape

Tensile strength Yield strength Elongation(a), Hardness, Modulus of elasticity or size when subjected to the appropriate defor- Condition MPa ksi MPa ksi % HB GPa 106 psi mation/thermal procedure are referred to as shape memory alloys (SMA). According to the Solution treated 620 90 240 35 40 145 165 24 Solution treated and aged3hat 1240 180 795 115 18 345 185 26.5 shape memory effect, an alloy that is shaped at 730 °C (1345 °F) a given temperature and then reshaped at an- Solution treated and cold 930 135 895 130 6 275 175 25.5 other temperature will return to the original worked 50% shape when it is brought back to the shaping Solution treated, cold worked 1380 200 1240 180 7 395 185 27 50%, and aged1hat730°C temperature. The shape memory effect is asso- (1345 °F) ciated with a martensitic transformation (see “Shape Memory Alloys,” Properties and Selec- (a) In 50 mm (2 in.) tion: Nonferrous Alloys and Special-Purpose Materials, Volume 2, ASM Handbook, for de- Table 16 Composition and thermal expansion coefficients of high-strength tails). controlled-expansion alloys The basis of the nickel-titanium system of SMA is the binary, equiatomic (49 to 51 at.% Coefficient of thermal expansion, from room temperature to: Inflection Ni) intermetallic compound of NiTi. This 260 °C (500 °F) 370 °C (700 °F) 415 °C (780 °F) temperature intermetallic compound is extraordinary be- Alloy designation Composition, % ppm/°C ppm/°F ppm/°C ppm/°F ppm/°C ppm/°F °C °F cause it has a moderate solubility range for ex- Incoloy 903 and 0.03 C, 0.20 Si, 37.7 Ni, 16.0 Co, 7.51 4.17 7.47 4.15 7.45 4.14 440 820 cess nickel or titanium, as well as most other Pyromet CTX-1 1.75 Ti, 3.0 (Nb + Ta), 1.0 Al, metallic elements, and it also exhibits a ductil- 0.0075 B, bal Fe ity comparable to most ordinary alloys. This Incoloy 907 and 0.06 C max, 0.5 Si, 38.0 Ni, 13.0 7.65 4.25 7.50 4.15 7.55 4.20 415 780 solubility allows alloying with many of the ele- Pyromet CTX-3 Co, 1.5 Ti, 4.8 (Nb + Ta), 0.35 Al max, 0.012 B max, bal Fe ments to modify both the mechanical properties Incoloy 909 and 0.06 C max, 0.40 Si, 38.0 Ni, 14.0 7.75 4.30 7.55 4.20 7.75 4.30 415 780 and the transformation properties of the system. Pyromet CTX-909 Co, 1.6 Ti, 4.9 (Nb + Ta), 0.15 Al Excess nickel, in amounts up to approximately max, 0.012 B max, bal Fe 1%, is the most common alloying addition. Ex-